1. Field of Invention
This invention relates to a method and apparatus for an evaporative fluid cooler as a closed circuit cooling tower where corrugated metal tube heat transfer elements are used to cool the fluid in the closed loop.
2. Description of the Prior Art
The prior art includes the use of closed loop cooling towers for applications including commercial air conditioning, and process cooling.
Commercial air conditioning, particularly in the southwestern United States, is a substantial portion of overall electrical power demand. Most commercial air conditioning equipment is installed as air-cooled roof top package units, where the radiant and reflective heat from the roof deck substantially reduces the performance of the equipment. The use of water cooling rather than air cooling can dramatically improve the efficiency of the equipment because the water temperatures may be as much as 50 degrees cooler than the roof top air, and because of the large heat load that may be removed through the evaporation of water. The dramatic reduction in condensing temperatures possible with evaporative fluid coolers, or closed circuit cooling towers can result in cooling efficiency increases on the order of 50% and higher. These savings result in significant savings of peak kilowatt power.
The performance of an evaporative cooling device is optimized at elevated temperatures when the demand for power is greatest, and the performance of conventional air cooled units is greatly diminished.
One embodiment of the current invention is a water cooled system which may be retrofitted to existing roof top systems in order to increase the operating efficiency of this equipment by as much as sixty percent. The retrofit package is comprised of a specially designed closed loop cooling tower, piping manifold, and compressor modules to upgrade the existing systems.
Cooling towers have been used for large chilled water systems for air conditioning for many years. More recently, cooling towers have been employed on smaller commercial and residential systems.
Vendors of prior art cooling tower equipment include Marley Cooling Towers (www.marleyct.com) and Delta Cooling (www.deltacooling.com)
U.S. Pat. No. 6,250,610 issued Jun. 26, 2001 to Flaherty describes a molded cooling tower for industrial process cooling and air conditioning systems. The cooling tower includes a molded tower shell and supports for a filler material.
U.S. Pat. No. 5,501,269 issued Mar. 26, 1996 to Jenkins describes a fiberglass cooling tower with an uplift air flow.
U.S. Pat. No. 6,122,922 to Conner, issued Sep. 26, 2000, describes a closed loop cooling tower with three modes of operation including direct air-cooled, direct liquid cooled, and indirect evaporative liquid cooled. One of the reasons for the complexity of that invention was to reduce the consumption of water in the cooling tower.
There is a need for a relatively simple and inexpensive closed circuit cooling tower that can conserve water by utilizing higher total dissolved solids water coolant, by utilizing untreated water, and can be operated without extensive chemical treatment of the coolant water in the tower. The application of evaporative cooling technology in light commercial and residential applications demands a low maintenance system. The design must allow service by untrained personnel at irregular internals. There is a need for a method and apparatus for the simple mechanical cleaning of heat exchange tubes in a closed circuit cooling tower by simple mechanical flexing of a corrugated stainless steel heat exchanger. The system should allow for freeze protection without the need for seasonal service and draining.
The current invention is a closed circuit cooling tower for evaporative fluid cooler applications such as water-cooled residential and commercial air conditioning, geothermal cooling supplementation, and process cooling applications. Typically, a first fluid which may be treated water or other fluids, is circulated between the closed circuit cooling tower and an application such as a condenser heat exchanger. Heat is transmitted from the application to the first fluid, and heat is removed from the first fluid at the cooling tower.
At the cooling tower, the first fluid is directed to a plurality of cooling tubes so that the fluid flows through the cooling tubes before being returned to the application. Heat flows from the first fluid through the walls of the cooling tube, and is partially removed by the evaporative cooling of a second fluid of the cooling tube. The second fluid is preferably water or non-potable gray water. In order to control corrosion and fouling, prior art cooling towers typically either treat the second fluid, or they have relatively high volumes of xe2x80x9cblow-downxe2x80x9d where a portion of the second fluid is removed, and fresh fluid is added.
In the current invention, the second fluid is preferably not treated, and preferably has little or no blow-down during operation. In the current invention, the second fluid can be untreated water, gray water, sea water or brackish water not suited for other applications. The design provides for very low maintance, low water consumption, due to its ability to handle very high concentrations of solids. The operating performance in the semi-arid regions is complemented by the fact that the machine conserves water relative to other evaporative devices.
The tubes are preferably flexible so that fouling can be mechanically removed by twisting and otherwise moving the tubes. A corrugated stainless steel tubing is a material which may be used effectively as heat exchanger tubes. The corrugations provide strength and flexibility during the cleaning operations, and they enhance the heat exchange at the outside surface of the tube. The stainless steel is resistant to corrosion, and can be subjected to acid cleaning without damage.
The current invention addresses the cost, maintenance, and water quality issues which have inhibited the acceptance of water-cooled units. An embodiment of the current invention is to use existing roof top units in place and to modify the units by installing a downsized compressor module with a freon to water heat exchanger. In one embodiment, the closed circuit cooling tower is installed with a piping loop to tie in all compressor modules to the closed loop. The units are converted from air-cooled systems to water-cooled units resulting in substantial energy savings and enhanced service life.
An embodiment of the current invention is a closed tower with a stainless steel heat exchanger design. The closed tower design allows for routine operation at much higher levels of total dissolved solids, or higher mineral concentrations than prior art cooling towers. This ability to run higher dissolved solids results in a dramatic reduction in blow down water losses, or bleed off to control mineral concentrations.
The flexible stainless steel heat exchanger can be cleaned of minerals by simply flexing each heat exchanger loop in a twisting motion. The mineral build up will break free and fall off of the heat exchanger.
The components in the cooling tower are preferably fiberglass, plastic, and stainless steel. This unique design allows for routine acid cleaning without damage to the tower or its components. The corrosion resistant materials of this equipment in areas with hard water consistent with many desert regions.
The cooling tower is resistant to freeze damage. Its catch basin is designed to freeze without being damaged by the expanding water. The catch basin shape is similar to an ice tray, thus allowing for expansion without damage.
The cooling tower may use non-potable gray water for cooling without damage or service problems.
The components, particularly the fiberglass housing and the corrugated stainless steel heat exchangers are also light weight so that they may be installed on most roofs without requiring structural modifications.